The present invention relates to a test system for testing an article of manufacture. More specifically, the present invention relates to testing and marking a printed circuit board.
When a printed circuit board is manufactured, it is often desirable to test various points in a circuit on the printed circuit board to determine whether the circuit is fully functional. Often, hundreds of test points on the circuit board must be selectively tested. This is generally accomplished using a printed circuit board tester, which typically includes a test fixture mounted in a tester that is electrically coupled to a computer. Generally, test fixtures have a large number of pins or have a large number of spring-biased test probes arranged to make, electrical contact with designated test points on the circuit board under test. The pins or probes are supported by a plate or multiple plates.
Any particular circuit laid out on a printed circuit board is likely to be different from other circuits. When the circuit to be tested is designed, a pattern of test points to be used in checking the circuit is selected. A corresponding array test pins or probes is then configured in the test fixture. This typically involves drilling a pattern of holes in the plate or plates to match the customized array of test pins or probes, and then mounting the test pins or probes in the drilled holes in the plate. The printed circuit board is then placed immediately adjacent the test fixture for testing. During testing, the ends of the test pins or probes are brought into contact with the test points in the circuit board under test. The other ends of the test pins or probes are electrically coupled to a test computer. Depending on the type of test fixture used, electrically coupling pins or probes to a test computer may be accomplished by a variety of methods. For instance, test pins in a test fixture may be pressed against a bed of nails that are electrically coupled to the test computer. In another application, each of the test probes in a test fixture may be hard-wired to connectors or transfer pins that transmit signals directly to and from the test computer.
Once the test pins or probes are brought into contact with the test points in the circuit board during testing, electrical test signals are transferred from the test computer through the test pins or probes to the board under test, and test signals are then transferred back to through the test pins or probes back to the test computer. The test computer detects continuity or lack of continuity between various test points in the circuits on the printed circuit board based on the test signals received. At the end of each test, the test computer produces a pass or a fail signal to indicate that tile board has either passed or failed the test.
After a test or a printed circuit board has been completed, it is desirable to indicate whether the tested circuit board is functional or whether it is not functional, based on whether the board passed or failed the test. It is typical to have an operator visually monitor the test computer. The operator then manually separates the good boards from the bad board based on the test results of the test computer. The good boards may be identified by manually stamping and identifying mark on the board. This method of indicating the outcome of a test has limitations. Relying on an operator is subject to operator error. Generally, experience has shown that some boards that were tested and shown to be bad boards as a result of the test, end up marked as good boards. Relying on operators to separate boards also adds an additional step that slows the testing process. It also risks the possibility of an operator inadvertently damaging the circuit board, which is typically sensitive to physical damage to the circuit board.
Various systems for automated marking of articles of manufacture are known. However, their applicability to printed circuit boards is limited. Many known systems mark an article of manufacture by etching or making other physical indentations on the article under test. This is not desirable in a printed circuit board, as etching or otherwise cutting into a printed circuit board often has a high degree of risk of damage.
Other marking systems rely on spraying and ink or paint and are simply too large and cannot perform adequately in the very limited space environment of a printed circuit board test system. Often, printed circuit boards carry many components and have many conductive paths. Because of the relatively dense population of conductive paths, there is very little space to mark the boards. A test system that overcomes the disadvantages of the prior art, would be desirable
The present invention is a testing and marking system for an article of manufacture such as a printed circuit board. The test system includes a test fixture, a control unit, and a marker assembly. After a component is manufactured, it is placed in proximity to the test system of the present invention. The test fixture is configured to receive test signals from the control unit and pass these signals through the circuit board and back to the control unit dependent on connections in the circuit board. The control unit then compares these signals to a stored netlist of a good board. The test signals received back from the circuit board are indicative of the condition of the circuit board. The control unit then generates a result signal The marker assembly is responsive to the result signal and is configured to mark the component in response to the result signal.